Along with the progress of a layered manufacturing technique also called a three-dimensional printing, the layered manufacturing technique has been used in various industrial fields. As the demand for a three-dimensional model increases, various sharing services appear in the web. As is the case in the precedent of MP3 and video markets, the increase of model sharing environments may pose a copyright problem for a three-dimensional printing environment model in the near future.
The three-dimensional model under a three-dimensional printing environment is available in a digital domain and has a special feature that the three-dimensional model is transformed into an analog form via a printing/scanning process. Therefore, the existing copyright protection techniques such as encryption, DRM and the like cannot be applied to an actually-printed three-dimensional model. A demand has existed for a copyright protection technique suitable for such a special situation.
There may be a situation that a three-dimensional model acquired by a three-dimensional scanner and released from copyright protection can be redistributed through the web or reproduced as an offline model via a three-dimensional printer. A three-dimensional watermark is a means for indicating a copyright by adding a human-unrecognizable distortion to a surface of a model and is a sole protection technique capable of maintaining copyright information even in a printing/scanning process.
The existing three-dimensional mesh watermarking is designed in conformity with different online applications and, therefore, has a problem in that it cannot operate in response to the distortion generated in a three-dimensional printing/scanning process. The distortions generated in a three-dimensional printing environment may be largely classified into three types. First of all, as shown in FIG. 1, a stair-step layering distortion is generated in a layered manufacturing process. Secondly, files and digital information including coordinate system information are all lost in a printing process. Lastly, various cuts and surface damages are generated in a scanning process.
Among the existing three-dimensional mesh watermarking methods, a non-blind method is very excellent in watermark detection performance because the non-blind method detects a watermark with reference to the information of an original model. However, it is necessary to refer to the information of an original model in order to detect a watermark. Therefore, the non-blind method is a quite impractical technique in that there is a need to build a database for a copyright-protected model.
Accordingly, a need has existed for a technique capable of detecting a watermark without referring to an original model.